Alveolar macrophage plasminogen activator.

Plasminogen activator is a neutral serine protease secreted by many different cells, including activated peritoneal macrophages, which can mediate both inflammation and fibrinolysis and perhaps cytolysis of tumor cells. Secretion of plasminogen activator by rabbit alveolar macrophages derived from normal animals and rabbits pretreated with bacillus Calmette-Guérin (BCG) to activate these macrophages was examined. Plasminogen activator was secreted into media of cultured alveolar macrophages, but was not present within the cells. Secretion, which was dependent upon the presence of viable cells, could be blocked by protein synthesis inhibitors and enhanced by concanavalin A and phorbol myristate acetate. The inhibition profile of rabbit alveolar macrophage plasminogen activator is consistent with that of a serine protease. Plasminogen activator is present in two forms with molecular weights of 28,000 and 45,000. Alveolar macrophage plasminogen activator was secreted in cultures from most rabbits (17 of 23) pretreated with BCG, but rarely in those from normal animals (2 of 14). Lavage fluids from many rabbits contained viable Bordetella bronchiseptica, but the presence of this organism showed no correlation with secretion of plasminogen activator. Rabbit alveolar macrophages secrete a plasminogen activator similar to that secreted by mouse peritoneal macrophages as described previously. Secretion is enhanced by activation of alveolar macrophage populations.